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Maintaining your Mercury outboard provides the peace of mind that your boat's motor will function properly when out for a day on the water. Oil changes are an important part of maintaining an outboard motor. Changing the lower unit oil of a Mercury outboard provides proper lubrication for the internal components of the motor while removing normal metal shavings from the oil. Checking the oil during the oil change will give you details on the state of the motor's internal components.
Items you will need
Oil drain pan
Gear oil tubes
Lower your Mercury outboard motor to its vertical position.
Slide an oil drain pan under the outboard's lower unit.
Turn the lowest plug on the lower unit counterclockwise with a flathead screwdriver to remove it from the outboard. Set the drain plug aside.
Remove the upper vent plug from the outboard by turning it counterclockwise with the flathead screwdriver. Set the vent plug aside as oil flows from the lower unit. Allow the oil to drain from the motor for one to two hours.
Inspect the oil in the drain pan. The oil should glitter with metal but contain no metal flakes.
Cut the end off a tube of gear oil with a utility knife. Push the open end of the gear oil into the opening for the lower drain plug. Squeeze the body of the tube to dispense oil into the lower unit. Continue opening tubes and dispensing until oil flows from the top vent plug opening.
Remove the tube from the drain plug opening. Align the upper vent plug with the top opening. Turn the vent plug clockwise to install it into the lower unit. Repeat the procedure to install the drain plug into the lower drain hole. Allow the oil to settle overnight.
Remove the top vent plug from the lower unit with the flathead screwdriver.
Add additional oil to the vent hole until the oil level reaches the bottom of the vent hole. Install the vent plug into the lower unit.